Step around half-open bomb (7)
I believe the answer is:
grenade
'bomb' is the definition.
(grenade is a kind of bomb)
'step around half-open' is the wordplay.
'step' becomes 'grade' (I am not sure about this - if you are sure you should believe this answer much more).
'around' is an insertion indicator.
'half' suggests halving the letters.
'open' with half the letters taken is 'en'.
'grade' placed around 'en' is 'GRENADE'.
Can you help me to learn more?
(Other definitions for grenade that I've seen before include "Small hand missile" , "Enraged (anag)" , "ultimate weapon" , "Angered (anag)" , "Small explosive that is thrown" .)